1. FIELD OF THE INVENTION
The invention relates to a circuit for indicating hard disk activity, and particularly to hard disk activity when the hard disk controller does not provide a specific activity signal.
2. DESCRIPTION OF THE RELATED ART
The performance demands on personal computers are ever increasing. It has been determined that a major bottleneck in improving performance is the capability to perform input/output (I/O) operations. Processor speeds continue to increase at a great rate and memory speeds and architectures can partially keep pace. However, the speed of I/O operations, such as disk and local area network (LAN) operations, has not kept pace. The increasing complexity of video graphics used in personal computers is also demanding greater performance then can be conventionally provided.
Some of the problems were in the bus architecture used in IBM PC-compatible computers. The EISA architecture provided some improvement over the ISA architecture of the IBM PC/AT, but more performance was still required. To this end Intel Corporation, primarily, developed the Peripheral Component Interconnect (PCI) bus. The PCI bus is a mezzanine bus between the host or local bus in the computer, to which the processor and memory are connected, and the I/O bus, such as ISA or EISA. For more details on the PCI bus, reference to the PCI Standard Version 2.0, from the PCI Special Interest Group in care of Intel Corp., which is hereby incorporated by reference, is advised. The bus was designed to have a high throughput and to take advantage of the increasing number of local processors that support I/O functions. For example, most disk controllers, particularly SCSI controllers, and network interface cards (NICs) include a local processor to relieve demands on the host processor. Similarly, video graphics boards often include intelligent graphics accelerators to allow higher level function transfer. Typically these devices have the capability of operating as bus masters, to allow them to transfer data at the highest possible rates.
One feature users have requested in personal computers is a hard disk activity LED. This LED provides an indicator to the users that the hard disk drive is in use, allowing the users a rough measure of system activity and a warning not to turn off the computer system. Originally, the LED was provided directly on the hard disk drive and visible to the user. In later computer system designs, the hard disk drive was not visible, so alternative designs had to be developed. Various alternatives included remote installation of the previous LED and the use of light pipes. In one alternative, the address bus was monitored for accesses to the standard hard disk drive registers and a one shot was triggered on each access. The one shot then drove the activity LED. In later computer systems, IDE or integrated drive electronics hard disk drives started being used. The IDE standard connection includes a line which is provided for the disk drive to drive a remote activity LED. So the IDE standard specifically provided are LED activity line.
One other development was the use of multiple hard disk drives in a disk array, which was logically addressed by the computer system as a single disk. A disk array controller received the logical commands and provided physical commands to the multiple hard disk drives. The disk array controller provided a dedicated output signal indicating disk drive activity. In one embodiment this output signal was provided to a reserved line on the EISA bus, with the computer system monitoring this line to drive the activity LED.
Thus, solutions were provided for several cases, particularly IDE drives and those in disk arrays. But problems existed for SCSI drive systems, because no dedicated activity line is available on the SCSI bus, and further complicated if the SCSI controller is a PCI bus device, as again no dedicated activity line is available on the PCI bus. Therefore, if the computer system used a PCI bus-based SCSI hard disk controller, the user could not monitor hard disk drive activity because the disk drive activity LED could not be driven.